London is a safer place after a "sophisticated criminal network" led by a former Army sergeant was jailed for a total of nearly 55 years, a police chief has said.

Former r oyal engineer Paul Alexander, 58, and his "business partner" Carl Gordon masterminded an operation to sell guns and ammunition to the criminal underworld from their prison cells at HMP Swaleside in Kent, where the pair were both serving life sentences, Scotland Yard said.

Gordon, 27, and Alexander, who was jailed in 2009 for making guns for gangs after a police crackdown following the murder of Liverpool schoolboy Rhys Jones, used smuggled mobile phones to arrange for family and others to buy obsolete firearms.

The weapons were then converted to live firearms and sold illegally, police said.

At Woolwich Crown Court yesterday, Alexander pleaded guilty to conspiracy to supply firearms with intent to endanger life. He was handed a 16-year sentence to run after his current jail sentence ends next year.

Alexander's wife, Caroline Hunter-Mann-Purdy, 64, of Harwich Road, Harwich, in Essex, pleaded guilty to conspiracy to supply firearms and was sentenced to seven years.

His step-daughter, Lullabell Purdy, 26, of Harwich Road, Harwich, pleaded guilty to money laundering offences and was sentenced to 300 hours of community service.

David Joseph, 28, of HMP Wandsworth, pleaded guilty to conspiracy to supply firearms and ammunition and was sentenced to 10 years.

Leon Brown, 31, of Melville Road, north-west London, pleaded guilty to conspiracy to transfer ammunition and was sentenced to three years and 10 months.

Following a trial, Sherika Abbott-Holder, 27, of Ashbourne Road, Ealing, west London, was found guilty of conspiracy to supply firearms with intent to endanger life and money laundering and sentenced to 11 years.

Emma Jones, 26, of Auriol Drive, Uxbridge, was found guilty of conspiracy to supply firearms and possession of a firearm and sentenced to seven years.

Detective Inspector Richard Mills of SCO7, the Met's Special Intelligence Section, said: "During the period that Gordon and Alexander met in prison, they effectively became business partners, dealing in deadly weapons and ammunition.

"The firearms and ammunition they converted had the potential to cause great harm on our streets and there is no doubt London is a safer place as a result of this network being dismantled.

"This was a complex investigation by the Met's Special Intelligence Section, which is committed to targeting criminal networks and bringing a successful prosecution. I would like to pay tribute to the detectives who have worked tirelessly to see this case to its successful conclusion."

Gordon, who is serving a life sentence for murder, is due to be sentenced at a later date.